Optical pick-up device for recording/reading information on optical recording medium

ABSTRACT

An optical pick-up device for recording/reading an optical recording medium is provided, which can efficiently utilize light emitted from the laser light source. The optical pick-up device includes a light source, an optical system, a quarter-wave plate, a diffraction component, and a photodetector unit. The photodetector unit may further include a transmitting portion for transmitting the light beam emitted from the light source, and may be disposed opposite the light source in a vicinity of the light source so that light emitted from the light source is transmitted through the transmitting portion. The transmitting portion may be an aperture provided in the photodetector unit. Alternatively, the optical pick-up device may further include an optical path separator for separating the diffracted returning light beam from the light beam that passes from the light source to the diffraction component.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an optical pick-up device having adiffraction component for recording/reading information on an opticalrecording medium such as an optical disk, an optical card, or an opticaltape.

[0003] 2. Description of Related Art

[0004] In the field of an optical pick-up device for recording/readinginformation on an optical recording medium such as a Compact Disk (CD),demands for simplification of structure, assembly, or adjustment, anddemands for reduction of costs have been increasing in recent years.

[0005]FIG. 21 illustrates a background optical pick-up device whichemploys a holographic diffraction component. The optical pick-up deviceincludes a semiconductor laser light source 511 for emitting laser lighthaving a wavelength of 780 nm, a photodetector unit 531, the holographicdiffraction component 553, a mirror 565, a reflective surface 566, adiffraction grating 541 for generating 3-division light beams, and anobjective lens 521. The laser light source 511, the photodetector unit531, and the holographic diffraction component 553 are integrated in abody tube, and are optically adjusted to form a block.

[0006] A light beam emitted from the laser light source 511 istransmitted through the diffraction grating 541 for generating3-division light beams and the holographic diffraction component 553, isreflected by the mirror 565 for bending the optical path, is transmittedby the objective lens 521, converges on a recording pit-surface of anoptical disk 101, and is reflected by the recording pit-surface.

[0007] The returning light beam thus reflected by the recordingpit-surface is transmitted through the objective lens 521, is reflectedby the mirror 565, and is incident onto the holographic diffractioncomponent 553, where two kinds of +1st order diffracted returning lightare generated by a holographic surface 554 having two differentholographic patterns with different pitches. These two kinds of beamsare incident on the reflective surface 566 at an angle equal to or morethan a critical angle, are thereby reflected by the total internalreflection, are transmitted through the transmitting surface after thetotal internal reflection, and arrive in the photodetector unit 531.Thereby, information signals, focusing-error signals, and tracking-errorsignals are detected.

[0008] According to the background optical pick-up device as shown inFIG. 21, the laser light source or the photodetector is capable of beingsubstituted to another one having a different specification. Therefore,modification by substitution of the component to another type ofhigh-speed photodetector or by adoption of a new type of semiconductorlaser light source can be easily achieved. Further, initial investmentsare not expensive for manufacturing products according to thisembodiment.

[0009] Another background optical pick-up device is disclosed in theJapanese Laid-Open Patent Publication No. 3-225636, which employs abirefringent diffraction component having a birefringent crystal forachieving high efficiency of light-utilization. FIG. 22 illustrates thebackground optical pick-up device which includes a semiconductor laserlight source 511 as a light source, a birefringent diffraction grating541 for separating a light beam 502 emitted from the semiconductor laserlight source 511 into three beams, a collimator lens 523 and anobjective lens 521, a birefringent holographic diffraction component555, a quarter-wave plate 625, a 6-division photodetector unit 532 fordetecting the diffracted returning light beam out of the optical axis,and a photodetector 533.

[0010] The collimator lens 523 and an objective lens 521 are used for animaging optical system. The light beam from the diffraction grating 541is collimated into parallel light beam and converges on an optical disk101 through the imaging optical system. The birefringent holographicdiffraction component 555 diffracts and separates the returning lightreflected by the optical disk 101 out of the optical axis of the imagingsystem. The quarter-wave plate 625 is disposed between the optical disk101 and the diffraction grating 541 or between the optical disk 101 andthe birefringent holographic diffraction component 555.

[0011] In this optical pick-up device, the birefringent holographicdiffraction component is used for simplifying the structure. Further, auniaxial structure of this optical pick-up device achievesminiaturization thereof and reduction in weight. In addition,reproduction of signals of the optical disk at high efficiency isachieved, when the birefringent holographic diffraction component andthe birefringent diffraction grating are employed.

[0012] As described above, by combining the semiconductor laser lightsource, the photodetector, and the holographic diffraction component, anoptical pick-up device-is provided having features accompanied by aminiaturized structure, a reduced weight, and a simplified method foradjustment. However, in the background optical pick-up device forrecording/reading, there still remain problems as follows.

[0013] (1) High efficiency in utilizing light is desired for recordinginformation on an optical recording medium. In an optical pick-up devicefor reading information on an optical recording medium such as a CompactDisc (CD), which is normally used for reproduction only, there are fewproblems regarding efficiency in utilizing light. In this case, thefocal length of the collimator lens may be long.

[0014] In contrast, in the optical pick-up device for recording are-writable or write-once optical recording medium such as a CompactDisc ReWritable (CD-RW), a Compact Disc Recordable (CD-R), a DigitalVideo Disc Recordable (DVD-R), or a Digital Video Disc ReWritable(DVD-RW), a collimator lens having a large numerical aperture and ashort focal length is frequently used for collecting light from thesemiconductor laser light source with little loss, in order to secure ahigh power of light on the surface of the optical disk.

[0015] However, when such a collimator lens having a short focal lengthis used, a space for disposing a mirror for reflecting the diffractedreturning light, etc., becomes narrow. Therefore, the mirror is requiredto be miniaturized. In this case, mass-productivity is deteriorated dueto difficulties in assembling such a miniaturized component accurately.

[0016] (2) A large separation angle is required. As described above, inachieving an optical pick-up device capable of recording, the collimatorlens having a large numerical aperture and a short focal length, forexample, a numerical aperture of 0.3 and a focal length of 10 mm, isfrequently used. In this case, for securing a package interval between alaser diode package and a photodetector package within such a shortdistance, a large diffraction angle of the diffraction grating shouldpreferably be employed, from this point of view.

[0017] For achieving the large diffraction angle of the diffractiongrating, a diffraction grating having a short pitch should be employed.In this case, however, due to restrictions in fabricating a gratinghaving such a short pitch, it is difficult to form an ideal gratingstructure having the short pitch.

[0018] As a result, a separation property for the polarized light ordiffraction efficiency is generally deteriorated, and a SIN ratio ofsignals is reduced. With this context, there have been limitations inemploying a diffraction grating having a reduced pitch, or largediffraction angle, in the background optical pick-up device.

[0019] (3) Divergent transmitted light is imposed on aberration due toanisotropy of substrate crystal. When the birefringent crystal substratesuch as a thin lithium niobate substrate is disposed in a divergentoptical path, because the refractive index depends on a propagationdirection of the light, the transmitted light is imposed on aberration.

[0020] Therefore, when the birefringent crystal is disposed between thelaser diode light source and the collimator lens, it is preferred thatthe aberration should be suppressed by disposing an additional opticalmember for suppressing the aberration. However, in this case, themanufacturing cost increases. Further, mass-productivity isdeteriorated, because the thin crystal substrate is not easilyprocessed.

[0021]FIG. 23A illustrates yet another background optical pick-up devicefor recording/reading information on a recording surface of an opticalrecording medium. The background optical pick-up device is explainedwith reference to FIGS. 23A-23C.

[0022] In FIG. 23A, a divergent light beam emitted from a light-emittingportion 513 of the semiconductor laser light source 511 as a lightsource is transmitted through the diffraction grating 551, and isincident onto the collimator lens 523 which collimates the light beaminto a parallel light beam. Subsequently, the light beam is reflected byan upward-reflection mirror 563, is transmitted by a quarter-wave plate625, begins to converge when it is transmitted through an objective lens521, and converges as a light spot on a recording surface 103 of anoptical recording medium 101 such as a Compact Disc, etc.

[0023] The returning light beam, which is reflected by the recordingsurface 103, is transmitted by the objective lens 521 and thequarter-wave plate 625, is reflected by the upward-reflection mirror563, begins to converges when it is transmitted through the collimatorlens 523, and is transmitted by the diffraction grating 551.

[0024] The diffraction grating 551 is a birefringent holographicdiffraction component for diffracting the returning light beam, whichhas a power of diffraction dependent on the polarization of the light. Aplane of polarization of the returning light beam after transmitted bythe quarter-wave plate 625 twice, or forth and back, is rotated by 90degrees from the initial state as emitted from the light source. Thebirefringent holographic diffraction grating 551 is constructed so asnot to diffract the light beam from the light source but to diffract thereturning light beam. By this diffraction, the returning light beam isseparated from the optical path between the light source and thediffraction grating 551. Then, the diffracted returning light beam isreflected by a mirror 565, to be incident on the photodetector unit 531.

[0025] The photodetector unit 531 generates focusing-error signals andtracking-error signals on the bases of the detection of the returninglight beam, and also generates reproduction signals for reproducinginformation. Further, by controlling an actuator (not shown) of aservo-system on the basis of the thus generated focusing-error signalsand the tracking-error signals, focusing/tracking operation isperformed.

[0026] As described above, the optical pick-up device which records orreproduces information of an optical recording medium requires a largepower of light beam when recording information. Therefore, theefficiency of light utilization from the light source is focused on foran optical pick-up device having such a structure as shown in FIG. 23A.

[0027]FIG. 23B illustrates a collimator lens 523 having a long focallength. When the focal length of the collimator lens 523 is long, evenif the separation angle t for separating the returning light beam isrelatively small, there are few problems in the layout of the mirror 565or the photodetector unit 531. However, because the emitted light beamfrom the semiconductor laser light source 511 is a divergent light beam,not a little portion of the emitted light beam is not collected by thecollimator lens 523, and the efficiency of light utilization of thepick-up device generally remains in a low level. Therefore, it becomesdifficult to perform operation for writing information at a high rate.

[0028] When numerical aperture of the collimator lens 523 is increasedfor utilizing light efficiently, in the optical pick-up device equippedwith a collimator lens 523 having a long focal length, the diameter ofthe collimator lens 523 is also increased, the dimension of the opticalpick-up device itself is therefore undesirably enlarged.

[0029]FIG. 23C illustrates a collimator lens 523 having a short focallength and a large numerical aperture. In this case, an amount of thelight beam collected by the collimator lens 523 is increased, inprinciple. However, a mirror 565 which reflects the returning light beamtoward the photodetector unit 531 is required to be disposed in aposition so as not to shield the divergent light beam emitted from alight-emitting portion 513. Therefore, a separation angle ζ should beset considerably larger than the separation angle ξ of FIG. 10B.

[0030] In order to increase the separation angle of the birefringentholographic diffraction component as a diffraction grating, a pitch ofthe grating has to be reduced. This requires, however, adoption of ahigh-level micro fabrication process, which in turn increases productioncosts, and by which mass-productivity is deteriorated.

[0031] If a diffraction grating having a small pitch, which is producedby a fabrication method without sufficient fabrication accuracy, isemployed, then poor quality in transparency or diffraction efficiencymay reduce power of the light projected on the optical recording mediumor the returning light beam. In this case, a problem may arise, forexample, a SIN ratio of the signals generated by the photodetector maybe reduced.

[0032] Further, in an optical pick-up device which employs abirefringent crystal such as a lithium niobate crystal, a transmittedlight beam, as far as it is divergent, is imposed on aberration, becauserefractive index of the birefringent crystal is dependent on propagationdirections of the light. The aberration may be compensated using acompensation optical component, but this further increases costs. Inaddition, the scale of the optical pick-up device becomes large.

[0033]FIG. 24 illustrates still another background optical pick-updevice, in which a holographic diffraction component is employed. Alaser light beam, which is emitted from a semiconductor laser lightsource 511, converges on an optical information recording medium such asan optical disk 101, through a holographic diffraction component 553 andan objective lens 523. Then, the returning light beam through theobjective lens 523 is diffracted by the holographic diffractioncomponent 553; thereby the returning light beam reflected by the opticaldisk 101 is separated from the light emitted from the semiconductorlaser 511.

[0034] A photodetector 531 detects the returning light beam which isdiffracted by the holographic diffraction component 553. Informationrecorded in the optical disk 101 is reproduced on the basis of signalswhich are obtained through detection of the returning light beam by thephotodetector 531.

[0035] Due to restrictions in manufacturing a holographic diffractioncomponent having a short pitch of grating, the background opticalpick-up devices frequently employ a holographic diffraction componenthaving a small angle of diffraction. As a result, the semiconductorlaser 511 and the photodetector 531 are arranged with a very closedistance, for example, in a range of 1-2 mm.

[0036] In this case, the following shortcomings may arise. First, noisemay be superimposed on signals of the photodetector 531, when thesemiconductor laser 511 is driven with a high-frequency modulation. Thisis typical in a photodetectors having a detection circuit therein, andmay deteriorate marginal detection of signals. Second, an opticalpick-up device is normally equipped with an optical unit which is packedwith semiconductor laser 511, holographic diffraction component 553, anda photodetector unit 531. In this case, modification of one unit bysubstitution of the unit, especially semiconductor laser 511, may not beeasy. Therefore, degree of freedom in designing is relatively low insuch an optical pick-up device.

SUMMARY OF THE INVENTION

[0037] Accordingly, the present invention has been made in view of theabove-discussed problems and an object of the present invention is toaddress these and other problems.

[0038] Another object of the present invention is to provide a noveloptical pick-up device capable of recording an optical recording mediumat high efficiency in light utilization.

[0039] According to an embodiment disclosed herein, a novel opticalpick-up device for recording/reading information on an optical recordingmedium is provided, which includes a light source for emitting a lightbeam, an optical system having a converging function for the light beam,a diffraction component, and a photodetector unit.

[0040] The light beam emitted from the light source converges on arecording surface of the optical recording medium through the opticalsystem, and the returning light beam that is reflected by the recordingsurface is collected and converges through the optical system. Thereturning light beam is diffracted by the diffraction component, andreaches the photodetector unit for detecting the diffracted light beam.The photodetector unit includes a detector for detecting the diffractedreturning light beam.

[0041] In another embodiment, the optical pick-up device may furtherinclude a quarter-wave plate. The quarter-wave plate is disposed in aposition so as to transmit the light beam and the returning light beam.A birefringent holographic diffraction grating is used in thediffraction component of this embodiment.

[0042] In yet another embodiment, the optical pick-up device may furtherinclude a monitoring detector for monitoring a power of the light beamemitted from the light source.

[0043] In still another embodiment, the photodetector unit furtherincludes a transmitting portion for transmitting the light beam emittedfrom the light source. The photodetector unit having the transmittingportion is disposed opposite the light source in a vicinity of the lightsource so that the light beam emitted from the light source istransmitted through the transmitting portion. The transmitting portionmay be an aperture provided in the photodetector unit.

[0044] In still another embodiment, the optical pick-up device furtherinclude an optical path separator for separating the diffractedreturning light beam from the light beam that is emitted from the lightsource toward the optical path separator. The optical path separatorincludes a transparent body having a surface having a reflective regionand a transmitting region.

[0045] The reflective region may reflect the light beam from the lightsource. Alternatively, the reflective region may reflect the diffractedreturning light beam diffracted by the diffraction component.

[0046] The transparent body may include a prism or a pair of prisms.Total internal reflection of the prism may be utilized in the reflectiveregion.

[0047] Alternatively, the transparent body may be a transparent flatplate which is disposed obliquely to an optical path of the returninglight beam. The optical pick-up device may detect tracking-error signalsusing an astigmatism focusing-error detecting method which utilizesastigmatism due to the flat plate.

[0048] In still another embodiment, the optical pick-up device furtherincludes an optical member having a prism-like transparent body which isdisposed in an optical path between the diffraction component and thelight source.

[0049] The optical member may include a reflective optical surfacethereon, which reflects the diffracted returning light beam toward thephotodetector unit. The light beam emitted from the light source may beprovided to the diffraction component through the optical member.

[0050] Alternatively, the optical member may include a first opticalsurface and a second optical surface formed on the optical member. Thefirst optical surface reflects but partly transmits the light beamemitted from the light source. The second optical surface reflects thediffracted returning light beam toward the photodetector unit, andtransmits the light beam that is transmitted through the first opticalsurface. The light beam that is transmitted through the second opticalsurface may be provided to the monitoring detector.

[0051] Yet alternatively, the optical member may include the firstoptical surface and a total internal reflection surface which reflectsthe light beam transmitted trough the first optical surface. The lightbeam that is reflected by the total internal reflection surface may beprovided to the monitoring detector.

[0052] In still another embodiment, the optical pick-up device furtherincludes a reflective member having a first reflective surface forreflecting the light beam emitted from the light source toward theholographic diffraction component and a second reflective surface forreflecting the diffracted returning light beam toward the photodetectorunit.

[0053] In other embodiments, the detector and the monitoring detectormay be integrated. Further, the optical pickup device may include areflective diffraction grating, which reflects a portion of the lightbeam emitted from the light source toward the monitoring detector.

[0054] In other embodiments, the diffraction component may include ablazed grating.

[0055] In other embodiments, the diffraction component may include aninorganic anisotropic optical film that is formed using an obliquedeposition method. Alternatively, the diffraction component may includean organic anisotropic optical film that is formed by orienting anorganic material.

[0056] In other embodiments, the light source, the diffractioncomponent, and the photodetector unit may be housed in a chassis.

[0057] In other embodiments, the diffraction component may furtherinclude an additional holographic converging function as a positivelens.

BRIEF DESCRIPTION OF THE DRAWING

[0058] A more complete appreciation of the present invention and many ofthe attendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0059]FIG. 1A illustrates an optical pick-up device according to anembodiment of the present invention;

[0060]FIG. 1B is a schematic view illustrating the photodetector unit ofFIG. 1A;

[0061]FIG. 1C is a schematic view illustrating a separation angle n ofthe diffraction component and a distance d between the photodetectorunit and the semiconductor laser light source of FIG. 1A;

[0062]FIG. 1D is a schematic view illustrating the diffraction componentof FIG. 1A;

[0063]FIG. 1E is a schematic view illustrating a photodetector of FIG.1A;

[0064]FIG. 2A illustrates a portion of an optical pick-up deviceaccording to another embodiment of the present invention;

[0065]FIG. 2B is a schematic view illustrating the optical pathseparator of FIG. 2A;

[0066]FIG. 3A illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention;

[0067]FIG. 3B is a schematic view illustrating the optical pathseparator of FIG. 3A;

[0068]FIG. 3C is a schematic view illustrating a substrate which may beemployed in a fabrication method of the optical path separator of FIG.3A;

[0069]FIG. 4A illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0070]FIG. 4B is a schematic view illustrating the optical pathseparator of FIG. 4A;

[0071]FIG. 5 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0072]FIG. 6 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0073]FIG. 7A illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0074]FIG. 7B is a schematic view illustrating the diffraction componentof FIG. 7A;

[0075]FIG. 8 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0076]FIG. 9 is a schematic view illustrating an oblique depositionmethod;

[0077]FIG. 10A is a schematic view illustrating a non-blazed diffractiongrating;

[0078]FIG. 10B is schematic views illustrating a blazed diffractiongrating;

[0079]FIG. 10C is a schematic view illustrating another blazeddiffraction grating having a step-like cross sectional structure;

[0080]FIG. 10D is a schematic view illustrating yet another blazedgrating having a step-like cross sectional structure;

[0081]FIG. 11 illustrates an optical pick-up device according to stillanother embodiment of the present invention;

[0082]FIG. 12 illustrates a portion of the optical pick-up device ofFIG. 11;

[0083]FIG. 13 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0084]FIG. 14A illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0085]FIG. 14B illustrates a photodetector of FIG. 14A;

[0086]FIG. 15 illustrates a portion of an optical pick-up deviceaccording to still embodiment of the present invention;

[0087]FIG. 16 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0088]FIG. 17 illustrates an optical pick-up device according to stillembodiment of the present invention;

[0089]FIGS. 18A and 18B are schematic views for the portion of theoptical pickup device of FIG. 17, illustrating directions of lightpropagation with and without rotational displacement of the reflectivemember, respectively;

[0090]FIG. 19 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0091]FIG. 20 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention;

[0092]FIG. 21 illustrates a background optical pick-up device using aholographic diffraction component;

[0093]FIG. 22 illustrates another background optical pick-up deviceusing a polarized holographic diffraction component;

[0094]FIG. 23A illustrates yet another background optical pick-up deviceusing a polarized holographic diffraction component;

[0095]FIG. 23B illustrates a portion of still another optical pick-updevice employing a collimator lens having a long focal length;

[0096]FIG. 23C illustrates a portion of still another optical pick-updevice employing a collimator lens having a short focal length; and

[0097]FIG. 24 illustrates still another background optical pick-updevice using a holographic diffraction component.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0098] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views,preferred embodiments of the present invention are now described.

[0099]FIG. 1A illustrates an optical pick-up device forrecording/reading information on a recording surface of an opticalrecording medium according to an embodiment of the present invention.The optical pick-up device includes a semiconductor laser light source11, a diffraction component 51, a collimator lens 23, anupward-reflection mirror 63, a quarter-wave plate 125, an objective lens21, and a photodetector unit 31. The semiconductor laser light source 11emits a light beam in a polarized state.

[0100] The optical pick-up device, as shown in FIG. 1A, recordsinformation on an optical recording medium 101 by irradiating arecording surface of the optical recording medium with a light beam fromthe semiconductor laser light source 11 through the diffractioncomponent 51, and reads information by irradiating the photodetectorunit 31 with a diffracted returning light beam through the diffractioncomponent 51. The collimator lens 23 and the objective lens 21 are usedto form an optical system, through which the light beam converges on therecording surface of the optical recording medium, and through which thereturning light beam that is reflected by the recording surface iscollected and converges. The optical pick-up device is further explainedwith reference to FIGS. 1A-1E.

[0101] A diffraction power of the holographic diffraction component 51for polarized light is dependent on a polarized state of light. In thisembodiment, the diffraction component 51 is constructed so as todiffract only the returning light beam.

[0102] The photodetector unit 31 includes a light transmitting portion37 and a detector 39 for detecting the diffracted returning light beam,as shown in FIG. 1B. In addition, the photodetector unit 31 is disposedin a vicinity of the semiconductor laser light source 11 so that thelight transmitting portion 37 is disposed opposite a light-emittingportion 13 of the semiconductor laser light source 11.

[0103] The collimator lens 23 collimates the diverging light beamemitted from the semiconductor laser light source 11. The opticalpick-up device according to this embodiment is capable of recordinginformation on an optical recording medium. Accordingly, the collimatorlens 23 is designed to have optical properties such that the light beamfrom the light source can be utilized efficiently. For example, acollimator lens having a focal length of 10 mm and a numerical apertureof 0.3 may be employed in this embodiment.

[0104] The photodetector unit 31 may have a substrate. The lighttransmitting portion 37 may be a hole provided in the substrate of thephotodetector unit 31. In this case, the substrate need not betransparent. Alternatively, the light transmitting portion 37 may bemade of a transparent material.

[0105] In this embodiment, the light transmitting portion 37 is formed,for example, as an aperture which is provided to have an ellipsoidoutline that fits on with that of the divergent light beam emitted bythe semiconductor laser light source 11, where the light transmittingportion 37 has a major axis having a length of, for example, 0.5 mm, sothat the whole light beam emitted from the light-emitting portion 13 canbe substantially transmitted through the light transmitting portion 37.In FIG. 1A, although the photodetector unit 31 and the semiconductorlaser light source 11 are illustrated separately, the photodetector unit31 may be disposed on a front surface of a package of the semiconductorlaser light source 11 using a bonding agent, etc.

[0106] The photodetector unit 31 is placed in a position near thelight-emitting portion 13 so that the light transmitting portion 37 ison the extension of the optical axis of the collimator lens 23, wherethe light-emitting portion 13 is also on the extension of the opticalaxis of the collimator lens 23. The light beam emitted from thelight-emitting portion 13 is transmitted through the light transmittingportion 37 and through the diffraction component 51, where thediffraction component 51 is configured to have no holographicdiffraction power for the light beam emitted from the light source tothe collimator lens 23. Then, the light beam is collimated by thecollimator lens 23, reaches an optical recording medium 101, and isreflected by the optical recording medium 101. The returning light beamthat is thus reflected by the optical recording medium 101 passesthrough the collimator lens 23, and is incident on the diffractioncomponent 51.

[0107] Because a plane of polarization of the returning light beam isrotated by 90 degrees from the initial state, the returning light beamis diffracted by the diffraction component 51, and is incident onto thedetector 39 of the photodetector unit 31. In FIG. 1A, the detector 39 isillustrated so that the detector 39 is disposed on the surface of thesubstrate. However, it is more preferable that the detector 39 is formedin a concave portion of the substrate, as illustrate in FIG. 1C.

[0108] In the embodiment as shown in FIG. 1D, the birefringentholographic grating 55 formed on the diffraction component 51 iscomposed of, for example, birefringent holographic portions A, B, and C.

[0109] Further, the birefringent holographic grating 55 having thebirefringent holographic portions A, B, and C may have a refractivefunction as a positive lens through which the diffracted returning lightbeam converges on the detector 39, because a distance between thedetector 39 and the diffraction component 51, with respect to theoptical axis, is smaller than that between the light-emitting portion 13and the collimator lens 23. In this embodiment, transverse direction, orright and left directions of FIG. 1A corresponds to a tracking directionof the optical pick-up device.

[0110] The detector 39 includes, as shown in FIG. 1E, 4-divisiondetector portions a1, a2, b, and c. A portion of the returning lightbeam diffracted by the birefringent holographic portion A converges on aboundary portion between the detector portions a1 and a2, and portionsof the returning light beam diffracted by the birefringent holographicportions B and C converge on the detector portions b and c,respectively.

[0111] Hereinafter, respective detected signal intensities being outputfrom the detector portions a1, a2, b, and c are expressed as signals α1,α2, β, and γ. In this embodiment, focusing-error signals are detected bythe knife-edge method, where the knife-edge portion is defined as aboundary portion between the birefringent holographic portions A and Bor between A and C. The focusing-error signals are given by (α1-α2)signals. If a spot of the light incident on the recording medium 101 isoff the track of the recording surface 103, the portion of the returninglight beam that is incident on the birefringent holographic portions Band C, varies asymmetrically. Therefore, (β-γ) signals may be used forthe tracking-error signals. As to the reproduction of information,(α1+α2+β+γ) signals or a portion thereof may be used as reproductionsignals.

[0112] As illustrated in FIG. 1C, an interval d between thelight-emitting portion 13 and the detector 39 of the photodetector unit31 may be as small as, for example, about 1 mm. In such a case, thenecessary separation angle η of the diffraction component 51 becomes,for example, about 10 degrees at most. Accordingly, a conventionalgrating may be used for the optical pick-up device according to thepresent invention, which includes a collimator lens having a largenumerical aperture. In this case, the above-mentioned problem does notarise, such as the decrease in an S/N ratio due to the deterioration ofseparation properties of polarized light, low efficiency in diffractionproperties, raised costs, or deterioration of mass-productivity. Inaddition, because the light transmitting portion and the detector areconstructed as an integrated unit, the photodetector unit 31 can beassembled with more ease than the case of the optical pick-up device ofFIG. 23, in which position of the mirror 565 relative to thephotodetector unit 531 has to be adjusted.

[0113]FIG. 2A illustrates a portion of an optical pick-up deviceaccording to another embodiment of the present invention. The opticalpick-up device according to this embodiment, includes a semiconductorlaser light source 11, a diffraction component 51, a photodetector unit41 having a detector, a collimator lens 23, an optical path separator131 for separating an optical path of the returning light beam from thatof a light beam emitted from the light source 11. A portion of theoptical system between an optical recording medium and the collimatorlens 23 is similar to that of the embodiment as illustrated in FIG. 1A.The optical pick-up device, as shown in FIG. 2A, records information onan optical recording medium by irradiating a recording surface of theoptical recording medium with a light beam emitted by the semiconductorlaser light source 11 through the diffraction component 51, and readsinformation by irradiating the photodetector unit 41 with a diffractedreturning light beam through the diffraction component 51. Thisembodiment is further detailed with reference to FIGS. 2A and 2B.

[0114] A light beam emitted from a light-emitting portion 13 of thesemiconductor laser light source 11 is reflected by the optical pathseparator 131, is transmitted through the diffraction component 51, andis collimated by the collimator lens 23. After that, the light beampasses through the optical path similar to that of the optical pick-updevice of FIG. 1A, and is incident on the recording surface of theoptical recording medium, in a form of a light spot. The returning lightbeam which is thus reflected by the recording surface passes in thereverse direction. Then, a plane of polarization of the returning lightbeam is rotated by 90 degrees from the initial state as emitted by thesemiconductor laser light source 11. Further, the returning light beamis transmitted through the collimator lens 23, is diffracted by thediffraction component 51, is transmitted through the optical pathseparator 131, and is incident onto the photodetector unit 41.

[0115] The optical path separator 131 separates optical path of thereturning light beam from that of the light beam emitted from thesemiconductor laser light source 11 to the diffraction component 51. Theoptical path separator 131 includes a transparent body, for example, aprism. As illustrated in FIG. 2B, there are a reflective region 132having a metal film and a transmitting region 133 in an oblique surfaceof the prism. The light beam emitted from the semiconductor laser lightsource 11 is reflected by the reflective region 132 toward thediffraction component 51, and the returning light beam diffracted by thediffraction component 51 is incident on the transmitting region 133, isthereby transmitted by the prism, and is finally incident on thephotodetector unit 41.

[0116] The diffraction component 51 is a birefringent holographicdiffraction component having a diffractive function dependent on thepolarization of light. As to the birefringent holographic grating formedon the diffraction component 51, a holographic grating similar to thatillustrated in FIG. 1D may be used.

[0117] The photodetector unit 41 detects the diffracted returning lightbeam that has been separated from the light beam from the laser lightsource 11. As to the photodetector unit 41, a detector having a detectorsurface similar to that illustrated in FIG. 1E may be used. In thisembodiment, because the photodetector unit 41 may be disposed in aposition where the returning light beam through the collimator lens 23converges, the birefringent holographic diffraction grating of thediffraction component 51 is not required to have a converging functionas a positive lens, in contrast to the embodiment as illustrated in FIG.1A.

[0118] According to the embodiment as illustrated in FIG. 2A, in whichthe reflective region 132 and the transmitting region 133 are formed onone surface of the optical path separator 131, the separation anglebetween the light beam and the returning light beam need not be large,because a boundary between the reflective region 132 and thetransmitting region 133 can be drawn accurately, in a case, for example,when the reflective region 132 and the transmitting region 133 areformed using a mask with sufficient accuracy. Thereby an optical pick-updevice capable of writing information on an optical recording medium isprovided without increasing the separation angle of the diffractiongrating. As a result, a low-cost mass productive conventionaldiffraction grating can be used for the writing optical pick-up device.

[0119] Further, according to the embodiment as shown in FIG. 2A, thesemiconductor laser light source 11 and the photodetector unit 41 may bedisposed with a sufficient distance, because the returning light beam isdiffracted by the prism along a direction apart from the semiconductorlaser light source 11. Thereby the photodetector unit 41 is not easilyinfluenced by heat from the semiconductor laser light source 11.

[0120]FIG. 3A illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention. Theoptical pick-up device according to this embodiment, includes asemiconductor laser light source 11, a diffraction component 51, aphotodetector unit 41, a collimator lens 23, an optical path separator135 for separating an optical path of the returning light beam from thatof a light beam emitted from the light source 11. A portion of theoptical system between an optical recording medium and the collimatorlens 23 is similar to that of the embodiment as illustrated in FIG. 1A.This embodiment is detailed with reference to FIGS. 3A-3C.

[0121] The optical pick-up device, as shown in FIG. 3A, recordsinformation on an optical recording medium by irradiating a recordingsurface of the optical recording medium with a light beam emitted fromthe semiconductor laser light source 11 through the diffractioncomponent 51, and reads information by irradiating the photodetectorunit 41 with a diffracted returning light beam through the diffractioncomponent 51.

[0122] In this embodiment, a birefringent diffraction grating is formedon the diffraction component 51 having a diffractive function dependenton the polarization of transmitted light.

[0123] The optical path separator 135 separates the optical path of thediffracted returning light beam from that of the light beam emitted fromthe semiconductor laser light source 11 to the diffraction component 51.A reflective region 136 and a transmitting region 137 are formed on asurface of the optical path separator 135 which is disposed in aposition such that the reflective region 136 reflect the light beam fromthe light source. The optical path separator 135 includes a transparentplate having two parallel surfaces, and is disposed obliquely to theoptical axis of the light beam. A reflective surface is formed on thereflective region 136 of the optical path separator 135, as shown inFIG. 3B, and the rest of the surface of the optical path separator 135corresponds to the transmitting region 137.

[0124] The photodetector unit 41 is disposed in the optical path of theseparated returning light beam so as to detect the returning light.

[0125] As a birefringent holographic diffraction grating of thediffraction component 51, the birefringent holographic diffractiongrating as explained with reference to FIG. 1D may be used. Further, thedetector as shown in FIG. 1E may be used in a photodetector unit 41. Inthis case, however, the birefringent holographic diffraction grating isnot required to have an additional convergence function as a positivelens, because the photodetector unit 41 may be disposed in a positioncorresponding to the conversion point of the returning light beamthrough the collimator lens 23.

[0126] In the embodiment as illustrated in FIG. 3A, the returning lightbeam through the transparent plate having two parallel surfaces isimposed on astigmatism, because the returning light beam is transmittedthrough the transparent portion of transparent plate that is disposedobliquely. In this case, this astigmatism may be used for theastigmatism-method for detecting focusing-error signals. If theabove-mentioned astigmatism is not sufficient for generating thefocusing-error signals, the holographic diffraction component may havean additional holographic function which enhances the astigmatism of thetransparent plate. Alternatively, the holographic diffraction componentmay have the reverse additional holographic function which cancels theastigmatism of the transparent plate, if another method for detectingfocusing-error signals is employed.

[0127] The dimension of the optical path separator 135 is in the orderof 3 mm×5 mm utmost, for example; and a mass productive process formanufacturing the optical path separator can be utilized with ease usinga patterning method for producing pieces of optical path separators 135from a transparent substrate having a large area, as shown in FIG. 3C.

[0128] The position where the returning light beam converges does notshift even if the optical path separator 135 shifts to a certain extent,unless the surface-direction is changed. This is because the distance ofthe light-transmission is unchanged by the positional shift of theoptical path separator 135. In contrast, the above described opticalpath separator 131 employed in the optical pick-up device of FIG. 2Ashould be disposed within prescribed accuracy in order to avoid problemsrelated to the positional shift.

[0129] In another embodiment, a light beam emitted from a light sourcemay be transmitted through a transparent surface of an optical pathseparator, and a diffracted returning light beam may be reflected by areflective surface of the optical path separator. In this case, thelight beam incident on the optical recording medium is also imposed onthe astigmatism. Therefore, this astigmatism on the recording surfacemay preferably be canceled using an optical means.

[0130]FIG. 4A illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention. Thisembodiment is further explained with reference to FIGS. 4A and 4B. Theoptical pick-up device according to this embodiment, includes asemiconductor laser light source 11, a diffraction component 51, aphotodetector unit 41, a collimator lens 23, an optical path separator141 for separating an optical path of the returning light beam from thatof a light beam emitted from the light source. A portion of the opticalsystem between an optical recording medium and the collimator lens 23 issimilar to that of the embodiment as shown in FIG. 1A. The opticalpick-up device, as shown in FIG. 4A, records information on an opticalrecording medium by irradiating a recording surface of the opticalrecording medium with a light beam from the semiconductor laser lightsource 11 through the diffraction component 51, and reads information byirradiating the photodetector unit 41 with a diffracted returning lightbeam through the diffraction component 51.

[0131] In this embodiment, the diffraction component is a birefringentholographic diffraction component having a diffractive functiondependent on the polarization of transmitted light.

[0132] As shown in FIG. 4B, the optical path separator 141 is a cubictype prism component having two right-angle prisms 142A and 142B whoseoblique surfaces are adhered to each other. Further, a reflectivesurface 143 is formed on a portion of the adhered surface. The rest ofthe adhered surface corresponds to a transparent surface 144.

[0133] In the embodiment as shown in FIG. 4A, a light beam emitted bythe semiconductor laser light source 11 is transmitted through theoptical path separator 141. Namely, respective positions of thesemiconductor laser light source 11 and the photodetector unit 41 areapproximately interchanged, in contrast to those of FIG. 3A. Accordingto this arrangement for the semiconductor laser light source 11 and thephotodetector unit 41, width of the optical pick-up device becomesgenerally smaller than that of the optical pick-up device of FIG. 2A or3A, where the width of the optical pick-up device, in this case,corresponds to the vertical direction of each figure. Thereby an opticalpickup device suitable for a notebook-type computer is provided, becausea width of a seek-rail thereof can be designed to be narrow. Further,because the cubic prism component, in which oblique surfaces of the tworight angle prisms are adhered each other, generates little aberrationon the transmitted light, the diffraction component 51 need not have theaforementioned additional holographic function to cancel the aberration.Thereby the birefringent holographic diffraction component may include aconventional grating having a simple lattice structure. In this case,production cost of the diffraction component 51 is low, and stability ofthe diffractive function is high.

[0134]FIG. 5 illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention. Theoptical pick-up device includes a semiconductor laser light source 11, adiffraction component 51, a photodetector unit 41, a collimator lens 23,an optical path separator 145 for separating an optical path of thereturning light beam from that of a light beam emitted from the lightsource. A portion of the optical system between an optical recordingmedium and the collimator lens 23 is similar to that of the embodimentas shown in FIG. 1A. The optical pick-up device, as shown in FIG. 5,records information on an optical recording medium by irradiating arecording surface of the optical recording medium with a light beam fromthe semiconductor laser light source 11 through the diffractioncomponent 51, and reads information by irradiating the photodetectorunit 41 with a diffracted returning light beam through the diffractioncomponent 51.

[0135] In this embodiment, the diffraction component 51 is abirefringent holographic diffraction component having a diffractivefunction dependent on the polarization of transmitted light.

[0136] The optical path separator 145 is a prism, and an internalreflection at its oblique surface 148 is utilized for separating opticalpaths of the light beam from that of the returning light beam. Namely,only one of these light beames is reflected by the total internalreflection of the oblique surface 148, according to the difference inincident angle. There are no reflective films formed on the obliquesurface 148, because the reflective region correspond to a region wherethe light is incident on the region with an incident angle such that thetotal internal reflection of the light takes place.

[0137] In the embodiment as shown in FIG. 5, the light beam emitted fromthe semiconductor laser light source 11 is incident onto the obliquesurface 148 with an incident angle of 45 degrees, with respect to themajor propagation direction. When a refractive index of the optical pathseparator 145 is 1.6, for example, an equation: 1.6 sin(45° )=1.13 (>1),stands. Thereby a condition for total internal reflection is satisfied.This condition is satisfied even when the divergence of the light beamis taken into account. Therefore, the whole light beam is reflected bytotal internal reflection. Further, when a diffraction angle of thediffraction component 51 is 10 degrees, for example, the returning lightbeam that is diffracted by the diffraction component 51 is incident ontothe oblique surface 148 with an incident angle of 35 (=45−10) degrees,with respect to the major propagation direction. In this case, anequation: 1.6 sin(35° )=0.92 (<1), stands. Thereby the diffractedreturning light is transmitted through the optical path separator 145.The condition is also satisfied even when divergence of the diffractedreturning light beam is taken into account.

[0138] Therefore, the reflective region of the optical path separator145 can be provided without forming any reflective films. Further, asshown in FIG. 5, the reflective region and the transmitting regionpartly overlap each other on the oblique surface 148 of the optical pathseparator 145. Thereby, the optical path separator 145 itself can beminiaturized. Furthermore, the optical pick-up device can employ alow-cost birefringent holographic diffraction component having a smallpitch of grating. Accordingly, costs are further reduced.

[0139]FIG. 6 illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention. Thisembodiment is a variation of the above-explained optical pick-up deviceof FIG. 4A, which is capable of monitoring a power of light. A portionof the optical system between an optical recording medium and thediffraction component 51 is similar to that of the embodiment as shownin FIG. 1A.

[0140] In general, the light beam emitted from the light source ispreferably controlled to be within a prescribed power range for a stableoperation of optical pick-up device. Therefore, intensity oflight-emission is optionally monitored by detecting a portion of theemitted light beam emitted from the light source. According to theembodiment as shown in FIG. 6, a monitoring detector 35 for monitoring apower of light is disposed between the diffraction component 51 and theoptical path separator 141. The monitoring detector 35 is necessary tobe arranged with high accuracy so that the monitoring detector 35 canreliably detect the portion of the light beam from the semiconductorlaser light source 11, and may not shield the returning light.Therefore, assembly of the monitoring detector 35 is slightly difficult.

[0141]FIG. 7A illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention. Thisembodiment is another variation of the above-explained optical pick-updevice of FIG. 4A, which is capable of monitoring a power of light. Adiffraction component 51A, as shown in FIG. 7B, is employed in thisembodiment. A reflective holographic grating 57 for reflecting a portionof a light beam emitted from a semiconductor laser light source 11 isfurther formed on the diffraction component 51A, in order to provide amonitoring light beam. The reflective holographic grating 57 is disposedadjacent to a birefringent holographic grating 56 for diffracting thereturning light beam. The reflective holographic grating 57 reflects aperipheral divergent light beam emitted from the semiconductor laserlight source 11, which is a portion not used for irradiation on theoptical recording medium. The light beam reflected by the reflectiveholographic grating 57 is further reflected by a reflective region ofthe optical path separator 141, and is incident onto a photodetectorunit 41A. The reflective holographic grating 57 also has a convergingfunction as a lens for convergence of the reflected, light beam on thephotodetector unit 41A. The photodetector unit 41A further includes amonitoring detector for detecting the monitoring light beam reflected bythe reflective holographic grating 57, as well as the detector fordetecting the returning light beam.

[0142] According to this embodiment, because the reflective holographicgrating 57 and the birefringent holographic grating 56 are integrated onthe diffraction component 51A with an accurate arrangement, positionaladjustment between them is not required, provided that the diffractioncomponent 51A is correctly disposed in a prescribed position. Therebythe optical pick-up device can be assembled with ease. Further, themonitoring detector for monitoring the light beam and the detector forthe returning light beam may be integrated in the photodetector unit41A. Further, when a large amount of monitoring light is required, sucha reflective holographic diffraction component may be formed in thewhole peripheral region.

[0143]FIG. 8 illustrates a portion of an optical pick-up deviceaccording to yet another embodiment of the present invention. Theoptical pick-up device includes a semiconductor laser light source 11, adiffraction component 51, a photodetector unit 41 having a detector, achassis 121, and an optical path separator 141 for separating an opticalpath of the returning light beam from that of a light beam emitted fromthe light source. A portion of the optical system between an opticalrecording medium and the diffraction component 51 is similar to that ofthe embodiment as shown in FIG. 1A. The semiconductor laser light source11, the diffraction component 51, the photodetector unit 41, and theoptical path separator 141 are arranged in respective positions of thechassis 121.

[0144] Miniaturization of the optical pick-up device is achieved byintegrating the semiconductor laser light source 11, the diffractioncomponent 51, the photodetector unit 41, and the optical path separator141 into the integrated cell-structure. Further, the optical componentsare effectively prevented from a relative positional error. In addition,an assembly of the optical pick-up device is facilitated because eachoptical component may be independently manufactured or assembled, andmay be integrated. Thereby modifications by substituting one or moreoptical components to the other improved optical components, such as asubstitution to a semiconductor laser capable of outputting a high powerbeam or to a detector having high sensitivity.

[0145] In the embodiment as shown in FIG. 8, the light source, thediffraction grating, the optical path separator, and the photodetectorunit are assembled to be integrated in the chassis. Specifically,optical components of any above-explained embodiment may be integratedin a chassis. For example, as to the integration of the optical pick-updevice of FIG. 1A, the semiconductor laser light source 11, thediffraction component 51, the photodetector unit 31 having the detectorand the light transmitting portion 37 which is disposed of opposite thelight-emitting portion 13 of the semiconductor laser light source 11,may be assembled to be integrated in respective positions of a chassis.

[0146] In each of the embodiments as illustrated in FIGS. 4A-8A,positions of the light source and the photodetector unit may beapproximately interchanged. For example, as an alternative to theembodiment of FIG. 5, the light beam emitted from the light source maybe transmitted through the transparent region of the optical pathseparator, and reaches the diffraction component 51. In this case, thereturning light beam diffracted by the diffraction component 51 isreflected by the optical path separator. In this embodiment, arrangementof respective optical components is slightly optimized, in order toachieve a suitable operation.

[0147] In each of the embodiments as illustrated in FIGS. 1A-8A, thediffraction grating is disposed between the light source and thecollimator lens. Specifically, the position of the diffraction gratingis not restricted to such a position. For example, the diffractiongrating may be disposed in any appropriate position between thecollimator lens and the quarter-wave plate.

[0148] As mentioned above, when the birefringent crystal such as lithiumniobate is used for the birefringent diffraction grating, the light, asfar as it is divergent, is imposed on aberration due to anisotropy ofrefractive index. When such a diffraction grating having a birefringentcrystal is employed, the diffraction grating is preferably disposed inan optical path of the parallel light beam.

[0149] In any case, the birefringent holographic diffraction componenthaving such a birefringent crystal is expensive, and increases costs.

[0150] As an alternative to such an expensive birefringent crystal, ananisotropic film made of an organic material or an inorganic materialmay be employed in the birefringent holographic grating in theembodiments according the present invention, for reducing costs orsuppressing aberration.

[0151] The inorganic birefringent film may be formed using a so-calledoblique disposition method.

[0152] For example, a method is disclosed in the Japanese publication,Journal of Surface Finishing Society of Japan, Vol. 46, No. 7,p32(1995). An anisotopic film having birefringence Δn of about 0.08 isobtained by depositing a dielectric material such as LiNbO₃ or CaCO₃ ona substrate by the oblique disposition method as illustrated in FIG. 9,where the birefringence Δn=n_(p)−n_(s) is defined by the differencebetween refractive indexes of P-polarized light (n_(p)) and S-polarizedlight (n_(s)). This value is equivalent to that of the LiNbO3 crystal.Further, because this film can be deposited on a substrate having alarge deposition area by the conventional disposition method, reductionof the production cost is achieved. In addition, because a thickness ofthe deposited film is very small, for example, in the order of 10 μm, incontrast with the LiNbO₃ crystal substrate having a thickness of about500-1000 μm, generation of aberration is suppressed considerably, evenwhen it is disposed in an optical path of divergent light.

[0153] Another method is known for forming a birefringent anisotopicfilm using an organic highly oriented film. The method is disclosed inthe publication, Journal of Applied Physics, Vol. 72, No. 3, p938(1992).

[0154] As an under-layer, an oriented film such as a SiO film, which isdeposited on a transparent substrate such as a glass substrate using anoblique deposition method, or an oriented polyethylene terephtalate(PET) film, which is treated by a rubbing using a cloth, is employed.Diacetylene monomer is deposited in an oriented state on the under-layerby a vacuum evaporation method. The oriented diacetylene monomer film isthen polymerized to form a birefringent anisotopic film by theirradiation of ultraviolet light. This vacuum evaporation method canalso produce an organic low-cost anisotopic film.

[0155] Still another method for producing a birefringent anisotopic filmis disclosed in the Japanese publication, TECHNICAL REPORT OF IEICE,EDM94-39, CPM94-53, OPE94-48 (1994-08), issued by the Institute ofElectronics, Information and Communication Engineers. Namely, apolyimide molecular chain is oriented uniaxially by the drawing of apolyimide film that is fabricated by a method such as a spin-coatmethod; thereby the birefringence is induced in the polyimide film withrespect to a direction of the film plain. According to this method, thebirefringence An can be varied by varying a manufacturing condition oftemperature or a value of force imposed on during the drawing process.This provides a mass productive low-cost method.

[0156] Accordingly, a birefringent holographic diffraction component isfabricated by, for example, (1) depositing the above-mentionedbirefringent film on a substrate such as a quartz-glass substrate, (2)cutting the substrate into pieces having a prescribed dimension, (3)forming a holographic pattern of concave or convex surface on respectivepieces of the substrate using an anisotropic etching method, etc., and(4) coating over the holographic pattern with an isotropic material forforming a flat surface of the isotropic material over the holographicpattern.

[0157] In the above-detailed embodiments, the returning light beam isdiffracted by the birefringent holographic diffraction component, and isincident onto the detector. To be more precise, the diffracted returninglight includes the fractions of light corresponding to +1st orderdiffracted returning light and −1st order diffracted returning light, asshown in FIG. 10A. However, only a +1st order diffracted returning lightreaches the detector in the above-explained embodiments. Intensity ofthe +1st order diffracted returning light is equal to that of the −1storder diffracted returning light, when a symmetrical diffraction gratingis used. Therefore, only a half of the diffracted returning light isdetected by the detector in embodiments using such a symmetricaldiffraction grating, and the other half is lost.

[0158] In contrast, when a blazed holographic diffraction component isemployed, the diffracted returning light beam can be utilized moreefficiently. Namely, as shown in FIG. 10B, a blazed grating may be usedas the diffraction grating. Alternatively, another blazed grating havinga step-like cross sectional structure may be used, as shown in FIG. 10Cor 10D.

[0159] In such a blazed grating, the cross-sectional features withrespect to a cross-section of the diffraction component becomeasymmetrical. Accordingly, intensity of the +1st order diffractedreturning light L1 is more intense than that of the −1st orderdiffracted returning light L2, and the optical pick-up device canutilize the diffracted returning light beam efficiently by placing thedetector in the position suitable for detecting the intensified +1storder diffracted returning light. The S/N ratio is thereby increased,and reliability is increased. In addition, an excellent signal detectingoperation can be achieved even for an optical recording medium drivenwith a high angular velocity.

[0160]FIG. 11 illustrates an optical pick-up device according to stillanother embodiment disclosed herein.

[0161] The optical pick-up device includes a semiconductor laser lightsource 11, a prism 71 as an optical member, a birefringent holographicgrating 55 on a diffraction component, a collimator lens 23, aupward-reflection mirror 63, a quarter-wave plate 125, an objective lens21, and a photodetector unit 31 having a plurality of detectors. In thisembodiment, the prism 71, which has a transparent body formed in a shapeof a square pole or a trapezoid-pole, is employed. A reflectiveprism-surface 73 as a reflective optical surface is formed on an obliquesurface of the prism 71 at one end. In FIG. 11, an optical disk 101 asan optical recording medium is also illustrated.

[0162] In FIG. 11, a light beam emitted from the semiconductor laserlight source 11 is transmitted through the prism 71 and the birefringentholographic diffraction component; 55, and is refracted by thecollimator lens 23 to become a parallel light beam. The parallel lightbeam becomes a circularly polarized light when passing through thequarter-wave plate 125. Then, the light beam which has been transmittedthrough the objective lens 21 converges on a recording surface of theoptical disk 101, in a form of a micro light spot, and is reflected bythe recording surface. The returning light beam, which is thus reflectedby the recording surface of the optical disk 101, returns to thecollimator lens 23 again via the objective lens 21 and the quarter-waveplate 125, in a form of linearly polarized light having a plane ofpolarization rotated by 90 degrees from that of the light as emittedfrom the semiconductor laser light source 11. The returning light beginsto converge when it is transmitted through the collimator lens 23, isdiffracted by the birefringent holographic diffraction component 55, isreflected by the reflective prism-surface 73, and is incident onto thephotodetector unit 31. Thereby information signals, focusing-errorsignals, and tracking-error signals are detected.

[0163] In this embodiment according to the present invention, the prism71 reflects the diffracted returning light from the birefringentholographic diffraction component 55 toward the photodetector unit 31,and is disposed so that the transmitting body between two parallelsurfaces is set in the optical path between the semiconductor laserlight source 11 and the birefringent holographic diffraction component55. For the embodiment as shown in FIG. 12, we let n and d denoterefractive index and thickness of the prism 71, respectively, then, thelength of optical path in the prism 71, through which the light istransmitted, becomes d/n. In this case, the interval between thesemiconductor laser light source 11 and the collimator lens 23 isincreased by (d−d/n) from that in the case without the prism 71, therebythe interval between the birefringent holographic diffraction component55 and the reflective prism-surface 73 may be designed larger, to theextent corresponding the above-explained interval increased.

[0164] For example, when the prism 71 is made of BK7-glass having arefractive index of 1.5 and a thickness of 0.3, equations d/n=2.0 mm and(d−d/n)=1 mm stand. Therefore, the length of optical path of thisportion may be shortened by 1 mm than in the case without the prism 71.Therefore, the space for another component is enlarged. Namely, in theoptical pick-up device without the prism 71, it requires a space havingan interval of 3 mm for disposing the reflective surface. In contrast,by disposing the prism 71 between the semiconductor laser light source11 and the birefringent holographic diffraction component 55, it hasequivalent effect as the case which requires reduced space of only 2 mmfor disposing the reflective mirror. Thereby the interval L between thebirefringent holographic diffraction component 55 and the reflectiveprism-surface 73 can be increased, and the birefringent holographicdiffraction component 55 having small separation angle θ may be employedin an optical pickup device for recording an optical recording medium.Therefore, deterioration of separation properties of the birefringentholographic diffraction component 55 for polarized light is suppressed,which generally arises when the birefringent holographic diffractioncomponent 55 has a small pitch, or a large separation angle.

[0165]FIG. 13 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention. Anexemplary optical system including a portion between the light sourceand the collimator lens or between the collimator lens and thephotodetector unit is illustrated. In this embodiment, a trigonal prism75 is employed as the prism-like optical member. The trigobal prism hasa first optical surface 75 a, a second optical surface 75 b, and a thirdoptical surface 75 c. The other potions are similar to those of FIG. 1A.

[0166] In FIG. 13, light emitted from the semiconductor laser lightsource 11 is reflected by the first optical surface 75 a of the trigonalprism 75, is transmitted by the birefringent holographic diffractioncomponent 55, and becomes parallel light when being transmitted by thecollimator lens 23. After that, similar to the embodiment of FIG. 11,the light is focused on the recording surface of the optical disk. Thereturning light, which is reflected by the recording surface, returns tothe birefringent holographic diffraction component 55 through thecollimator lens 23, is diffracted by the birefringent holographicdiffraction component 55, is reflected by the second optical surface 75b of the trigonal prism 75, and is incident onto the photodetector unit31 having a detector for detecting information signals and a monitoringdetector for monitoring a power of light, thereby information signals,focusing-error signals, and tracking error signals are detected.

[0167] According to this embodiment, the photodetector unit 31 cansimultaneously detect the power of light beam emitted from thesemiconductor laser light source 11, as well as the information signals.Namely, the light emitted by the semiconductor laser light source 11 isnot perfectly reflected by the first optical surface 75 a, but isslightly transmitted by the first optical surface 75 a. Thereby, aportion of the light emitted by the semiconductor laser light source 11passes through the first optical surface 75 a, is reflected by the thirdoptical surface 75 c, is transmitted by the second optical surface 75 b,and is incident on the photodetector unit 31.

[0168] In this embodiment, for example, the second optical surface 75 bmay be constituted of polarized beam splitter, which reflectsS-polarized light and transmits P-polarized light. Because the lightdiffracted by the birefringent holographic diffraction component 55 isS-polarized light and the light passes inside the trigonal prism 75 isP-polarized light, the light diffracted by the birefringent holographicdiffraction component 55 is reflected by the second optical surface 75 btoward the photodetector unit 31, and the monitoring light which passesinside the trigonal prism 75 is transmitted by the second opticalsurface 75 b, and reaches the photodetector unit 31.

[0169]FIG. 14A illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention. In thisembodiment, the reflective prism-surface 73 of FIG. 11, which reflectsthe diffracted returning light, is substituted to a reflectivediffraction grating 73′, for example, as shown in FIG. 14A. The lightfrom the birefringent holographic diffraction component 55 is dividedinto three beams of 0th order light and ±1st-order light. As shown inFIG. 14A, the +1st order beam images at a pre-focus point before thesurface of the photodetector unit 31, and the −1st order beam images ata rear-focus point after the surface of the photodetector unit 31. Whenthe photodetector unit 31 has respective 3-division photodetectors 31 a,31 b, and 31 c for detecting the +1st order beam, the −1st order beam,and the 0th order beam, focusing-error signals may be detected by thebeam-size method. In this case, the 3-division photodetector 31 cdetects the 0th order beam.

[0170] According to the above-described constitutions of the reflectivediffraction grating 73′, the birefringent holographic diffractioncomponent 55 is not required to be divided into complicated dividedpatterns. In addition, adjustment in assembling process is facilitatedin this case.

[0171] Further, because the spot size of the 0th order diffractedreturning light on the photodetector unit 31 is small when the 0th orderdiffracted returning light from the reflective diffraction grating 73′is used for information signals detection only, the 3-divisionphotodetector 33 c for detecting the 0th order diffracted returninglight can be designed to be small. Therefore, when the 3-divisionphotodetector 33 c further includes a high-speed amplifier, high-speedRf signals having high quality are obtained, according to theabove-described constitution suitable for high-speed signals.

[0172] Also, when the second optical surface 75 b of the trigonal prism75 in the embodiment as shown in FIG. 13 may be substituted to therefractive type diffraction grating. In this case, the similar effect isobtained.

[0173]FIG. 15 illustrates a portion of an optical pick-up deviceaccording to still another embodiment of the present invention. Anexample of the optical system, which include a portion between the lightsource and the collimator lens or a portion between the collimator lensand the photodetector unit, is illustrated. In this embodiment, atrigonal prism 76 having a first optical surface 76 a, a total internalreflection surface 76 b, and a third optical surface 76 c is employed,and both of the signal light and the monitoring light are simultaneouslydetected by the photodetector unit 31. A portion between the collimatorlens 23 and the optical recording medium is similar to that of theembodiment as shown in FIG. 13.

[0174] In FIG. 15, light emitted by the semiconductor laser light source11 is reflected by the first optical surface 76 a of the trigonal prism76, is transmitted by the birefringent holographic diffraction component55 and collimator lens 23, and becomes parallel light. After that, thelight converges on the recording surface of the optical disk as in thecase of the embodiment as illustrated in FIG. 11, and the reflectedreturning light returns to the birefringent holographic diffractioncomponent 55 after being transmitted through the collimator lens 23.Then, the returning light is diffracted by the birefringent holographicdiffraction component 55 to be incident onto the photodetector unit 31,thereby information signals, focusing-error signals, and tracking-errorsignals are detected.

[0175] In this embodiment, because the first optical surface 76 a of thetrigonal prism 76 is configured so as to transmit light slightly, aportion of the light emitted by the semiconductor laser light source 11is transmitted through the first optical surface 76 a, is reflected bythe total internal reflection surface 76 b, is transmitted through thethird optical surface 76 c to be projected outside the prism, and isincident onto the photodetector unit 31. Thereby, signal light andmonitoring light can be detected using the photodetector unit 31. Incontrast with the embodiment of FIG. 13, special optical surface such aspolarized beam splitter surface of the second optical surface 75 b ofthe trigonal prism 75, which reflects signal light and transmitsmonitoring light, is not required for this embodiment. Therefore,production of the triangle prism is facilitated, and the costs arereduced.

[0176] In embodiments, with the same context as explained with referenceto FIGS. 10B-10D, a blazed diffraction grating may be used for thebirefringent holographic diffraction component 55. This asymmetricalstructure increases amount of the diffracted returning light thatreaches the photodetector unit 31, thereby a S/N ratio of the signals isimproved, or excellent signal detection is achieved for optical diskdrives for driving optical recording medium with a high-speed rotation.

[0177] In the above mentioned embodiments, the semiconductor laser lightsource, the member, the birefringent holographic diffraction component55, and the photodetector unit 31 may be integrated in one chassis toform a cell-structure. FIG. 16 illustrates a portion of an opticalpick-up device, in which the semiconductor laser light source 11, thebirefringent holographic diffraction component 55, the photodetectorunit 31, and the prism-like optical member 71 having a reflectivesurface are housed at respective prescribed positions in the chassis121. Such a cell-structure is advantageous in achieving as follows:

[0178] 1. miniaturization;

[0179] 2. stabilizing positional errors of respective components; and

[0180] 3. facilitating assembly of the optical pick-up device.

[0181] In addition, both of reduction of costs and high reliability areachieved, because equivalent stability as the background hologram unit,which includes a mirror tube in which a laser diode light source and aphotodetector unit are incorporated, is obtained.

[0182]FIG. 17 illustrates an optical pick-up device according to stillanother embodiment of the present invention. The optical pick-up deviceincludes a holographic diffraction component 53, a semiconductor laserlight source 11, an objective lens 22, a photodetector unit 31, and areflective member 61. In this embodiment, the reflective member 61 isprovided among the semiconductor laser light source 11, holographicdiffraction component 53, and photodetector unit 31. The reflectivemember 61 is, for example, isosceles-trigonal prism, which includes afirst reflective surface 61 a and a second reflective surface 61 b. Thefirst reflective surface 61 a reflects a laser light beam emitted fromthe semiconductor laser light source 11 to the holographic diffractioncomponent 53. The second reflective surface 61 b reflects the returninglight beam, which is diffracted by the holographic diffraction component53. Thereby the diffracted returning light beam is separated from thelight beam emitted from the laser light source 11, and reaches thephotodetector unit 31.

[0183] According to the optical pick-up device having such a structure,even if the diffraction angle of the holographic diffraction component53 is small, a marginal distance between the semiconductor laser lightsource 11 and the photodetector unit 31 is obtained by interposing thereflective member 61 in the optical path between the semiconductor laserlight source 11 and the photodetector unit 31 or between thephotodetector unit 31 and the holographic diffraction component 53.Therefore, the photodetector unit 31 can be disposed in a position suchthat the photodetector unit 31 is not hardly influenced by the effect ofhigh-frequency from the semiconductor laser light source 11, because thesemiconductor laser light source 11 and the photodetector unit 31 arenot necessarily disposed closely. Further, because the semiconductorlaser light source 11, the photodetector unit 31, and the reflectivemember 61 are no longer required to be packed together when they aremanufactured/shipped, each optical component can be facilitated to bedesigned with high degrees of freedom, thereby the optical pick-updevice itself can be designed with high degrees of freedom.

[0184] Further, because the light is reflected twice by the firstreflective surface 61 a and the second reflective surface 61 b of thereflective member 61, the effect of rotary displacement of thereflective member 61 on the light, with respect to the incident side andthe projected side, is canceled. Therefore, the optical system is noteasily influenced by the rotary displacement. This is further explainedwith reference to FIGS. 18A and 18B. FIG. 18A illustrates respectivepropagation directions of the laser light in a normal state without therotary displacement of the reflective member 61. Both of the light Pfrom the semiconductor laser light source 11 to the first reflectivesurface 61 a and the returning light S from the second reflectivesurface 61 b to the photodetector unit 31 is directed in respectiveprescribed directions, for example, in the same direction as illustratedin FIG. 18A.

[0185] In contrast, FIG. 18B illustrates respective propagationdirections of the laser light, when the reflective member 61 is rotatedat an angle with the rotary displacement. In this case, the propagationdirection of the reflected light q′, which is reflected by the firstreflective surface 61 a, inclines by 2θ with respect to the direction ofthe original reflected light q. Further, the reflected light r′ from theoptical recording medium 101 is also inclined at an angle 2θ withrespect to the direction of the original reflected light r. Therefore,the same angular relationship between the light P and the reflectedlight S is maintained, regardless of the existence of the rotarydisplacement of the reflective member 61. Namely, there arises nopositional displacement of the beam-spot position on the photodetectorunit 31. Thereby, errors in detecting focusing-error signals ortracking-error signals may not arise. Such a relationship is notrestricted to the above-described embodiment, in which the reflectivemember 61 is an isosceles-trigonal prism, and in which the light P andthe reflected light S are parallel.

[0186] Still another embodiment of the present invention is explainedwith reference to FIG. 19. The same reference numeral is used for eachcorresponding part to the embodiment as illustrated in FIG. 18A, and afurther explanation on the corresponding parts is abbreviated. Thisembodiment further includes a monitoring detector 35 for detecting aportion of the emitted light beam P′ from the semiconductor laser lightsource 11, which is not reflected by the first reflective surface 61 a.The light beam P′ is illustrated with slanted lines in the figure.

[0187] In order to record/reproduce information of the optical recordingmedium, it is necessary to operate with accurate output power of thelight beam from the semiconductor laser light source 11. According tothis embodiment, output power of the semiconductor laser light source 11can be detected accurately without loss, by detecting the emitted lightbeam P′ from the semiconductor laser light source 11, which is notreflected by the first reflective surface 61 a and is not used forrecording/reproducing. Thereby, a precise operation forrecording/reading information is realized.

[0188] In this embodiment, the photodetector unit 31 and the monitoringdetector 35 may be integrated on the same substrate 123, as shown inFIG. 20. Namely, the detector region for the photodetector unit 31 andthe detector region for the monitoring detector 35 are formed on thesubstrate 123. Adoption of such a substrate 123 effectively reducesnumber of components, thereby a low-cost and compact optical pick-updevice is provided. Further, according to the above-explainedembodiments, a novel optical pick-up device is provided, which candetect an accurate power of the light emitted from the semiconductorlaser for controlling the power thereof. Further, an optical pick-updevice is provided, in which number of parts is reduced.

[0189] Obviously, numerous modifications and variations of theembodiments disclosed herein are possible in light of the aboveteachings. It is therefore to be understood that within the scope theappended claims, the invention may be practiced otherwise than asspecifically described herein.

[0190] This document is based on Japanese Patent Application Nos.10-176959/1998 filed in the Japanese Patent Office on Jun. 24, 1998,10-189171/1998 filed in the Japanese Patent Office on Jul. 3, 1998, and10-199176/1998 filed in the Japanese Patent Office on Jul. 14, 1998, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. An optical pick-up device for recording/readinginformation on an optical recording medium, comprising: a light sourcefor emitting a light beam; an optical system having a convergingfunction for the light beam, through which the light beam converges on arecording surface of the optical recording medium, and through which thereturning light beam that is reflected by the recording surface iscollected and converges; a diffraction component for diffracting thereturning light beam that is reflected by the recording surface; and aphotodetector unit having a detector for detecting the diffractedreturning light beam and a transmitting portion for transmitting thelight beam, and being disposed opposite the light source in a vicinityof the light source so that the light beam emitted from the light sourceis transmitted through the transmitting portion.
 2. The optical pick-updevice according to claim 1, further comprising a quarter-wave plate,wherein the diffraction component is a birefringent holographicdiffraction component.
 3. The optical pick-up device according to claim2, wherein the diffraction component further includes a holographicconverging function as a positive lens.
 4. The optical pick-up deviceaccording to claim 2, wherein the transmitting portion is an apertureprovided in the photodetector unit.
 5. An optical pick-up device forrecording/reading information on an optical recording medium,comprising: a light source for emitting a light beam; an optical systemhaving a converging function for the light beam, through which the lightbeam converges on a recording surface of the optical recording medium,and through which the returning light beam that is reflected by therecording surface is collected and converges; a diffraction componentfor diffracting the returning light beam that is reflected by therecording surface; an optical path separator for separating thediffracted returning light beam from the light beam that is emitted fromthe light source toward the optical path separator, including atransparent body having a surface having a reflective region and atransmitting region on the surface; and a photodetector unit having adetector for detecting the diffracted returning light beam, and beingdisposed in an optical path of the diffracted returning light beam so asto detect the diffracted returning light beam.
 6. The optical pick-updevice according to claim 5, further comprising a quarter-wave plate,wherein the diffraction component is a birefringent holographicdiffraction component.
 7. The optical pick-up device according to claim6, wherein the reflective region reflects the light beam emitted fromthe light source.
 8. The optical pick-up device according to claim 6,wherein the reflective region reflects the returning light beamdiffracted by the diffraction component.
 9. The optical pick-up deviceaccording to claim 6, wherein the transparent body is a prism.
 10. Theoptical pick-up device according to claim 6, wherein the transparentbody is a transparent flat plate, which is disposed obliquely to theoptical path of the returning light beam.
 11. The optical pick-up deviceaccording to claim 10, wherein the photodetector unit detectsfocusing-error signals using an astigmatism focusing-error detectingmethod.
 12. The optical pick-up device according to claim 11 wherein thediffraction component includes an additional holographic function thatenhances an astigmatism due to the transparent flat plate.
 13. Theoptical pick-up device according to claim 10, wherein the diffractioncomponent includes an additional holographic function for canceling anastigmatism due to the transparent flat plate.
 14. The optical pick-updevice according to claim 6, wherein the transparent body is a pair ofprism-elements whose respective oblique surfaces are adhered each other,and wherein the reflective region is formed in a portion of the adheredoblique surfaces.
 15. The optical pick-up device according to claim 6,wherein the transparent body is a prism, in which a total internalreflection on an oblique surface of the prism is utilized for areflection of the reflective region.
 16. The optical pick-up deviceaccording to claim 2, further comprising a monitoring detector formonitoring a power of the light beam emitted from the light source. 17.The optical pick-up device according to claim 16, further comprising areflective holographic grating, which reflects a portion of the lightbeam emitted from the light source to provide a monitoring light beam,is formed in a vicinity of the diffraction component.
 18. The opticalpick-up device according to claim 2, wherein the diffraction componentincludes a blazed diffraction grating.
 19. The optical pick-up deviceaccording to claim 2, wherein the diffraction component includes ananisotropic optical film.
 20. The optical pick-up device according toclaim 2, wherein the light source, the diffraction component, and thephotodetector unit are housed in a chassis, thereby an integrated bodyis formed.
 21. The optical pick-up device according to claim 5, whereinthe light source, the diffraction component, the photodetector unit, andthe optical path separator are housed in the chassis, thereby anintegrated body is formed.
 22. An optical pick-up device forrecording/reading information on an optical recording medium,comprising: a light source for emitting a light beam; an optical systemhaving a converging function for the light beam, through which the lightbeam converges on a recording surface of the optical recording medium,and through which the returning light beam that is reflected by therecording surface is collected and converges; a diffraction componentfor diffracting the returning light beam that is reflected by therecording surface; an optical member having a prism-like transparentbody, which is disposed in an optical path between the diffractioncomponent and the light source, and through which the light beam isprovided to the diffraction component; a reflective optical surfaceformed on the optical member, which reflects the diffracted returninglight beam; a photodetector unit for detecting the diffracted returninglight beam that is reflected by the reflective optical surface.
 23. Theoptical pick-up device according to claim 22, further comprising aquarter-wave plate, wherein the diffraction component is a birefringentholographic diffraction component.
 24. The optical pick-up deviceaccording to claim 22, wherein the reflective optical surface is areflective diffraction grating.
 25. The optical pick-up device accordingto claim 22, wherein the diffraction component includes a blazeddiffraction grating.
 26. The optical pick-up device according to claim22, wherein the light source and the photodetector unit, and the opticalmember are housed in a chassis, and are fixed in respective prescribedpositions.
 27. The optical pick-up device according to claim 23, whereinthe diffraction component includes an anisotropic inorganic optical filmthat is formed using an oblique deposition method.
 28. The opticalpick-up device according to claim 23, wherein the diffraction componentincludes an anisotropic optical film that is formed by orienting anorganic material.
 29. An optical pick-up device for recording/readinginformation on an optical recording medium, comprising: a light sourcefor emitting a light beam; an optical system having a convergingfunction for the light beam, through which the light beam converges on arecording surface of the optical recording medium, and through which thereturning light beam that is reflected by the recording surface iscollected and converges; a diffraction component for diffracting thereturning light beam that is reflected by the recording surface; anoptical member having a prism-like transparent body, which is disposedin an optical path between the diffraction component and the lightsource; a first optical surface formed on the optical member whichreflects but partly transmits the light beam emitted from the lightsource; a second optical surface formed on the optical member, whichreflects the diffracted returning light beam, and transmits the lightbeam that is transmitted through the first optical surface; aphotodetector unit for detecting the reflected-diffracted returninglight beam that is reflected by the second optical surface.
 30. Theoptical pick-up device according to claim 29, further comprising aquarter-wave plate, wherein the diffraction component is a birefringentholographic diffraction component.
 31. The optical pick-up deviceaccording to claim 29, further comprising a monitoring detector formonitoring a power of the light beam emitted from the light source. 32.The optical pick-up device according to claim 29, wherein the secondoptical surface is a reflective diffraction grating.
 33. The opticalpick-up device according to claim 29, wherein the diffraction componentincludes a blazed diffraction grating.
 34. The optical pick-up deviceaccording to claim 29, wherein the light source and the photodetectorunit, and the optical member are housed in a chassis, and are fixed inrespective prescribed positions.
 35. The optical pick-up deviceaccording to claim 30, wherein the diffraction component includes ananisotropic inorganic optical film that is formed using an obliquedeposition method.
 36. The optical pick-up device according to claim 30,wherein the diffraction component includes an anisotropic optical filmthat is formed by orienting an organic material.
 37. An optical pick-updevice for recording/reading information on an optical recording medium,comprising: a light source for emitting a light beam; an optical systemhaving a converging function for the light beam, through which the lightbeam converges on a recording surface of the optical recording medium,and through which the returning light beam that is reflected by therecording surface is collected and converges; a diffraction componentfor diffracting the returning light beam that is reflected by therecording surface; an optical member having a prism-like transparentbody, which is disposed in an optical path between the diffractioncomponent and the light source; a first optical surface formed on theoptical member which reflects but partly transmits the light beamemitted from the light source; a total internal reflection surfaceformed on the optical member, which reflects the light beam transmittedthrough the first optical surface with total internal reflection; aphotodetector unit for detecting the reflected-diffracted returninglight beam that is reflected by the second optical surface.
 38. Theoptical pick-up device according to claim 37, further comprising aquarter-wave plate, wherein the diffraction component is a birefringentholographic diffraction component.
 39. The optical pick-up deviceaccording to claim 37, further comprising a monitoring detector formonitoring a power of the light beam emitted from the light source. 40.The optical pick-up device according to claim 37, wherein the secondoptical surface is a reflective diffraction grating.
 41. The opticalpick-up device according to claim 37, wherein the diffraction componentincludes a blazed diffraction grating.
 42. The optical pick-up deviceaccording to claim 38, wherein the light source and the photodetectorunit, and the optical member are housed in a chassis, and are fixed inrespective prescribed positions, thereby forming an integrated body. 43.The optical pick-up device according to claim 38, wherein thediffraction component includes an anisotropic inorganic optical filmthat is formed using an oblique deposition method.
 44. The opticalpick-up device according to claim 38, wherein the diffraction componentincludes an anisotropic optical film that is formed by orienting anorganic material.
 45. An optical pick-up device for recording/readinginformation on an optical recording medium, comprising: a light sourcefor emitting a light beam; an optical system having a convergingfunction for the light beam, through which the light beam converges on arecording surface of the optical recording medium, and through which thereturning light beam that is reflected by the recording surface iscollected and converges; a photodetector unit for detecting thereturning light beam; a diffraction component for diffracting thereturning light beam from the objective lens so that the diffractedreturning light beam is separated from the light beam; a reflectivemember having a first reflective surface for reflecting the light beamemitted from the light source toward the diffraction component and asecond reflective surface for reflecting the diffracted returning lightbeam toward the photodetector unit;
 46. The optical pick-up deviceaccording to claim 45, further comprising a monitoring detector whichmonitors a power of a portion of the light beam that is not reflected bythe reflective member.
 47. The optical pick-up device according to claim46, wherein the photodetector and the monitoring detector areintegrated.